A door closer is typically attached to a hinged door such as a front door, fire door, etc. of a house, apartment, officetel, etc. so as to automatically close the door by elastic force when it is opened. FIG. 1 is a cross-sectional view showing an example of a conventional door closer. Referring to FIG. 1, the conventional door closer comprises a housing 2, a pinion gear 4 which is fixed to a link shaft (also called a gear shaft) penetrating approximately the middle of the housing 2 and coaxially rotates with the link shaft, a coil spring 9 which is disposed on one side of the inside of the housing 2, and a spring pusher 6 which comprises a rack gear portion 7 engaged with the pinion gear 4 and pressurizes the coil spring 9 to accumulate elastic energy for closing a door (not shown) when the door is opened. The housing 2 is attached to the door, one end of a link (also called a connecting rod) is connected to the link shaft (not shown), and the other end of the link is connected to a door frame.
In the conventional door closer 1 shown in FIG. 1, the housing 2 has a space for accommodating the pinion gear 4 approximately in the middle thereof, a space for accommodating the coil spring 9 on one side thereof, and a space for accommodating the spring pusher 6 on the other side thereof. Therefore, the housing 2 cannot be easily configured compactly and reduced in size.
Meanwhile, a longer coil spring 9 having large elastic force is needed to close a heavy and large door such as a steel fire door. One side of the housing 2 is closer to a rotation axis (not shown) of the door than the other side of the housing 2, and thus it is difficult to provide a space for accommodating the large coil spring 9 by extending one side of the housing 2 in the positive (+) direction of the X axis. Moreover, the position of the pinion gear 4, i.e. the link shaft (not shown), is associated with the length of the link, which restricts the movement in the negative (−) direction of the X axis, and thus it is difficult to provide a space for accommodating the large coil spring 9 by extending the other side of the housing 2 in the negative (−) direction of the X axis. In other words, when a longer coil spring 9 is used to increase the door-closing force or efficiency in the conventional door closer 1, the link shaft (not shown) structurally needs to be more far away from the rotation axis of the door such that the door can be fully opened to 180° or the link needs to be configured longer, which is problematic.